Form This specification covers a premium aircraft-quality@ low-alloy@ heat-resistant steel in the form of bars@ forgings@ mechanical tubing@ and forging stock. Application These products have been used typically for parts such as compressor discs@ turbine discs@ shafts@ and fasteners for use in service up to 1000 ??(538 ?? and subject to stringent magnetic particle inspection standards@ but usage is not limited to such applications.